Unfortunately, hard shells used to close a motor vehicle bed are limited by their maximum inner height available. When, in fact, one needs to transport a cargo with a greater height than the one of the hard shell, the latter must be removed from the motor vehicle.
In order to solve this problem, folding shells have been devised, whose ends slide in rails fixed to the edges of the motor vehicle bed sides. Examples of these folding shells are described in U.S. Pat. No. 4,252,363, in U.S. Pat. No. 4,789,196, in U.S. Pat. No. 5,531,497, in U.S. Pat. No. 6,431,634, in USA Patent Application no. 2004/061351, in U.S. Pat. No. 6,997,502 and in Canadian Patent Application no. 2 638 493.
In particular, U.S. Pat. No. 6,997,502 describes a transformable cover for vehicles with bed, comprising means for detachably attaching said truck bed cover to the open bed, means for adjusting the length of said truck bed cover and a cover assembly detachably attached to said means. Said means for detachably attaching said truck bed cover to said open bed comprise two anchor rails and two cover attachment rails. The means for adjusting the height and the length of the truck bed cover comprise a plurality of support assemblies pivotally and slidably engaged with the anchor rails. Each of the plurality of support assemblies comprises two sled assemblies, two side members, two support cylinders and a third cross member. But these folding shells, being soft, need supports that partially occupy the useful cargo space. Moreover, they do not offer the advantage to last in time and they do not have suitable thermal isolation, mechanical rigidity and protection against acts of vandalism.